This invention relates to xe2x80x9cslow-releasexe2x80x9d materials and to a process for controlling the diffusion rate at which a slow-release material diffuses from a substrate or carrier. One application of the invention is for drip irrigation, and more particularly, drip irrigation devices having a controlled release rate of a herbicide that inhibits root growth. The invention extends the useful life of the drip irrigation product.
There are products in the marketplace which depend upon slow-release technology. An example is described in U.S. Pat. No. 5,116,414 to Burton et al. in which trifluralin (also referred to herein by the name Treflan, a trademark of Dow Agrosciences) is slowly released from a polymer into soil to inhibit root intrusion into that area. Another example is flea repellent dog collars where an insecticide is slowly released from the polymer in the collar. There are examples of slow-release or xe2x80x9csustained releasexe2x80x9d systems for other insecticides as well. A further example is South African Patent No. 86/1133 to Ruskin in which trifluralin is slowly released from a buried drip irrigation device in order to inhibit root intrusion into the device. (The Burton et al. and Ruskin patents are incorporated herein by this reference.)
In many cases more of the active material is released than is needed to efficiently meet the product requirements, whereas a lower rate of diffusion through the polymer would result in a longer product life. For instance, the active sustained release material, such as an insecticide, may be volatile and diffuse from the carrier device too rapidly, shortening retention life. A shortened retention life also can be a problem in the area of drip irrigation.
More specifically, drip irrigation devices which are often used in buried applications inhibit root intrusion by incorporating a herbicide such as trifluralin into the in-line drip emitter. Experience has shown success in protection of such buried drip irrigation devices from root penetration lasting for periods of many years. In addition to incorporating the Treflan (or other bioactive chemical) into the drip emitter per se, the herbicide or other bioactive material can be incorporated into a drip irrigation tube or tape. In any case, the bioactive chemical is incorporated into a polymer matrix which protects the bioactive chemical from chemical or biological degradation while providing a controlled but sustained release of the bioactive material to the soil adjacent the device for a substantial period of time, typically lasting many years.
The performance and life expectancy of such root growth inhibiting drip irrigation devices can be measured in terms of release rate or diffusion rate of the bioactive chemical from the host polymeric matrix in which it is bound. One of the drawbacks of present polymeric carrier delivery systems using trifluralin as a root growth inhibiting chemical is that diffusion rate or release rate of the chemical is difficult to sustain over long periods of time in a thin-walled product. That is, diffusion rate of the bioactive chemical from the host polymer is a function of the ratio of volume to surface area. For thin-walled products containing trifluralin, for example, essentially all of the trifluralin diffuses or migrates to the surface. This results in a shorter useful life of the product compared with a product of this invention in which the diffusion rate to the surface is reduced. Expected life of such thin-walled products can be extended by the present invention. Typically, products will have an increase of life expectancy of as much as 60%, so a thin-walled product of about 8 mils may increase from 5 to 8 years life, while a thicker product of 40 mils may increase from 20 to 32 years.
By way of example, with this invention drip irrigation products having a wall thickness on the order of about 8 mils, in which the impregnated bioactive chemical is trifluralin and in which the host polymer carrier is polyethylene, may have an expected life of about 20 years. (Laboratory tests can be conducted on various polymeric carrier materials containing bioactive chemicals at a certain wall thickness to estimate their stable rate of diffusion and then measure the expected life of the product.) It would be desirable to provide a long-term controlled release polymeric carrier delivery system which can extend the life expectancy of drip irrigation devices, and more particularly, to extend the useful life of thin-walled drip irrigation products by slowing the diffusion rate of bioactive chemicals such as trifluralin contained in such devices.
A more complete description of the present technology for preventing root intrusion in drip irrigation devices containing slow-release herbicides is presented in xe2x80x9cProtection of Buried Drip Irrigation Devices from Root Intrusion through Slow-Release Herbicides,xe2x80x9d Van Vories, et al., published in the Proceedings of the Fourth International Micro-Irrigation Congress at Albury-Wadonga, Australia, Oct. 23-28, 1988. Use of similar slow-release technology in subsurface drip irrigation devices applied to waste water, irrigation and drainage systems is reported in xe2x80x9cSub-surface Drip Irrigation Can Reduce Pollution,xe2x80x9d R. Ruskin, Proceedings of the Irrigation and Drainage Division of the American Society of Civil Engineers, Park City, Utah, Jul. 21-23, 1993. These publications are incorporated herein by this reference.
Referring again to the Burton et al. ""414 patent, and the slow-release technology disclosed in that reference, column 10, lines 10 et seq. disclose protecting a zone with 2 ppm trifluralin at 2 cm after 30 days. With the present invention adapted for drip irrigation use, intrusion of root growth in a hole approximately 2 to 2-xc2xd mm in diameter is protected. That is, 2 ppm trifluralin protection at about 2 mm from the dripper is all that is necessary, and therefore, the present invention requires a slower release rate (compared to Burton ""414) because of the smaller zone of protection.
Briefly, the invention is characterized by a slow-release product comprising a polymeric carrier, a slow-release active material dispersed in the carrier, and a fine particulate inert inorganic material dispersed in the carrier. The slow-release active material is diffusable from the carrier to produce an active function at a controllable level exterior to the polymeric carrier. The inorganic particulate material is dispersed in the resinous matrix to an extent sufficient to reduce the diffusion rate of the slow-release material to the exterior of the carrier, while the reduced diffusion rate is still sufficient to maintain an effective level of activity exterior to the carrier.
One embodiment of the invention comprises a slow-release product comprising a polymeric carrier or substrate, a slow-release material dispersed in the polymeric carrier, and an intercalation material in fine particulate form comprising an inert inorganic material having a layered structure dispersed in the polymeric carrier material. The slow-release material is dispersed between the layers of the intercalation material. The dispersed inorganic particles slow the diffusion rate of the slow-release material from the polymeric carrier.
In one embodiment, the intercalation material is a nano-clay, and the slow-release material is a bioactive material such as a herbicide to protect against root intrusion in drip irrigation applications, for example. The herbicide can comprise dinitroanaline. The bioactive material can comprise herbicides having other active functions, or alternatively, the bioactive material can comprise an insecticide that diffuses to the exterior of the polymeric carrier to produce its active function.
For drip irrigation applications in which the bioactive material is a herbicide, the slow-release product can comprise a drip irrigation emitter, or tape, or tube, or device used adjacent to an emitter to protect against root intrusion. The product also can be formed as a discontinuous bead along a drip irrigation tape, sheet or tube to protect drip emitters located in the vicinity of the beads.
In one embodiment of a drip irrigation product, an emitter made from a polymeric material containing a herbicide and the dispersed intercalation material is adapted for use in an irrigation supply tube or conduit. The supply tube can be a standard flexible plastic tubing, or it can include an inner lining containing a dispersed bactericide, as described below.
Another embodiment of the invention comprises a method for reducing the rate of diffusion of a slow-release active material through a host polymer material to increase the useful life of a slow-release product. The method comprises incorporating an intercalation material, comprising an inert fine particulate inorganic material having a layered structure, into a mixture of the slow-release bioactive material and the host polymer. The slow-release material is accommodated within spaces between the layers of the intercalation material sufficient to slow the diffusion rate of the slow-release material through the host polymer when compared with the diffusion rate of the same slow-release material through the same host polymer not containing the dispersed intercalation material.
One form of the invention comprises a drip irrigation emitter comprising a polymeric substrate base, a slow-release bioactive material dispersed in the substrate for inhibiting root growth in the vicinity of the emitter during use, and a fine particulate inorganic material dispersed in the substrate in an amount sufficient to reduce the release rate of the bioactive material from the emitter during use.
In one embodiment, the drip irrigation product includes a bactericide dispersed in the substrate in an amount sufficient to inhibit bacterial activity in the emitter during use. The bactericide can be incorporated into the dripper along with the slow-release bioactive material (herbicide). The bactericide also can be incorporated into a lining for the drip irrigation supply tube for killing slime-forming bacteria. The emitter containing the bactericide can be incorporated into drip irrigation supply tubes either of the conventional type (with no lining) or with a lining containing a bactericide.
In another embodiment, a slow-release product comprises a polymeric carrier, a slow-release active material dispersed in the polymeric carrier, and an intercalation material in fine particulate form comprising an inert inorganic material with a layered structure, in which molecules of the slow-release material are contained within the spaces between the layers of the intercalation material so as to inhibit the diffusion rate of the slow-release active material from the polymeric carrier. The intercalation material may be surface-treated to expand the spaces between the platelets that form the dispersed material. The active material is released at a controlled reduced rate, but at a level sufficient to maintain its effectiveness, while the resinous carrier maintains its structural properties.
These and other aspects of the invention will be more fully understood by referring to the following detailed description and the accompanying drawings.